1. Field of the Invention
The present invention relates to an electric motor and, more particularly, to a brush holder device for resiliently pressing brushes into sliding contact with a commutator.
2. Description of the Related Art
In general, an electric motor of the type described has brush holder devices each having a brush holder and a brush movably received in the brush holder, with a spring acting between the bottom of the holder and the brush so as to resiliently press the brush into contact with a commutator ring. In order to obtain a large effective area of contact between each brush and the commutator ring, the brush has a substantially rectangular cross section with a considerable dimension in the axial direction of the motor. On the other hand, the spring usually has a generally cylindrical form so that it is often experienced that a large clearance is formed between the brush holder wall and the spring in the direction of the axis of the motor, with the results that the spring is buckled or bent as shown in FIG. 5 or, when a plurality of springs are used, entangled. It is also to be pointed out that, when the brush holder device is assembled, the spring is set in an inclined posture. As a consequence, the state of contact between the brush and the commutator is impaired due to inadequate application of the spring force.
In order to overcome these problems, it has been proposed to use a special spring having an oval or elliptic cross section. The use of such a special spring, however, is not preferred because it has to be designed and produced exclusively for each brush holder, resulting in increased cost.